Electrodeposition of nickel



Patented Dec. 12, 1950 ELECTRODEPOSITION OF NICKEL William B. Stoddard,in, Hamilton, Ohio, as-

Signor to The Champion Paper and Fibre Com pany, Hamilton, Ohio, acorporation of Ohio No Drawing. Application January 8, 1946, Serial No.639,869

3 Claims. 1

This invention relates to the electrodeposition of nickel and hasparticular reference to methods of procuring deposits of specifiedhardness by suitably controlling the composition of the plating bath andthe conditions of electrodeposition. It has particular utility in theelectrodeposition of nickel for the purpose of building up and salvagingundersized metal parts and in the electroformation of nickel parts ofvarious types and specifically in the electroformation of nickel sheetsor strips of considerable size.

In the usual nickel platingart, the primary interest has been insecuring good adherence to the base metal, in avoiding porosity of thedeposit, and in recent yea-rs in obtaining nickel deposits which arebright as deposited and require no butting. Such deposits are in generalquite thinusually less than 0.001 inch in thickness-and the decorativefeatures are important. The physical properties, such as tensilestrength, ductility, etc. in such deposits are normally of littleinterest.

It is evident from the physical characteristics of metallic nickel thatit would be highly useful as a material for electrolytically building upundersized or worn parts by deposition on bearing or wearing surfaces,and for electroforming objects or machine parts which are subject towear or mechanical stress, if it were possible to accuratelypredetermine and satisfactorily control the physical properties of theelectrodeposit so that the desired strength hardness, and other physicalproperties, could be dependably secured and uniformly maintained withinthe required limits. Examples of parts which could be salvaged byproperly controlled electrodeposition of nickel thereon, are rotatingand sliding bearings and various parts subjected to wear and more orless localized pressure, impact and/or vibration. Electroformation, ifit could be properly controlled, would find util ty in the production ofwide variety of parts dillicult to construct with the desiredproperties, by conventional methods.

Endless nickel belts have been proposed for the continuous casting ofcellulosic or other films or of coating on paper as described in PatentNo. 1,719,166. Belts for these purposes must possess a uniquecombination of physical properties. They must have a relatively hightensile strength and yet stand repeated flexing around the necessarypulleys without damage. The surface must be smooth and must be hardenough not to be marred by the action of press rolls or any other actionincident to normal use. The belt must also be substantially uniform inthickness and in physical properties throughout its extent. Rollednickel belts have not been available in sufiicient width, length,quality, and uniformity to meet the requirements of this art.Electrodeposition has for some time been considered as ofiering adesirable method oiforming such belts, but so far as I amv aware theyhave not hereto fore been successfully produced in the required sizeswith the desired strength and hardness and the necessary uniformity.

I have now discovered that by properly selecting and controlling thecomposition of the elec trolytic bath and the conditions ofelectrodeposition, it is possible to deposit nickel of substantiallyuniform physical properties and to secure deposits of any predetermineddesired degree of strength, hardness, and ductility, within rather widelimits. Of course, as is well known, these properties are notindependently variable, but greater hardness is accompanied by highertensile strength and lower ductility, and measurements of hardness,because of their convenience and non-destructive nature, are commonlyused as an indication of strength. Hence accurate control of thehardness may be used as a means for securing deposits of predetermined,uniform strength and ductility within narrow tolerances, even where widevariations in hardness itself are permissible.

It is known to be possible by use of solutions containing considerableproportions of ammo.- nium chloride, to secure nickel deposits whichpossess a high degree of hardness. My process, however, operates to givedeposits of controlled predetermined hardness within a range somewhatbelow that of these highly hard deposits. a range wherein satisfactorypredetermination and control of hardness has not heretofore beenpossible, and which covers values of strength, hardness, resistance toimpact, and freedom from brittleeness which render the deposits highlyuseful in electroformed objects which must possess considerablestrength, and in reclaiming worn or mismachined parts which havehardness within this range for resistance to wear, shock, and fatigue.In order to secure deposits of such predetermined physical properties, Iuse a modification of the well known Watts bath containing the formatsradical in addition to the usual nickel sulfate, nickel chloride, andboric acid{ and to precisely control and maintain constant the con 3 ofthe factors included in the formula.

3 d tions of deposition, primarily the composition of the bath, the pH,the current density, and agitation of the bath. in using a bath of tiiscone position I have discovered that, within the limits of operation andwith all other conditions unchanged: 1. A higher ratio of formate tototal nickel gives a deposit of greater hardness and higher tensilestrength; 2. A higher pH value gives a deposit of greater hardness andhigher tensile strength; 3. A higher current density gives a deposit oflesser hardness and lower tensile strength; 4. A higher degree ofagitation of the a v=[50o.4+s0o roizsm gmg which V is Vickers hardness,CD is the oathode current density in amperes per square foot,

IEv is the ratio of formate to total nickel in the bath, and A is anagitation factor which has a value of about 1.0 for moderate agitationand a value from 1.6 to 2.0 or more for vigorous or turbulent agitation.It should be noted that this formula is only known to hold within limitswhich may be roughly expressed as follows: V between 100 and 400; Fbetween 0.1 and 0.5 (though at high values of pH and of nickel content,saturation may be reached at values of F below 0.5) pH between 2.0 and3.5; and CD bev tween 120 and 30.

The results obtained pursuant to the above formula are subject tofurther Variation to some degree with variations in other factors notincluded there-in, such as temperature, purity of the chemicals, andproportions of the ingredients in the bath-other than the ratioofformate to total nickel. Differences from the specified hardness whichmay result from differences from the assumed values in the abovefactors, can be cor rected by an appropriate change in one or more Ifthe conditions as determined by the formula, when degree of hardness,one or more of'the conditions can be altered as required to secure thedesired physical properties. The conditions to be changed and thedirection and approximate magnitude of the change required can be seenby inspection of the formula.

,For example, the hardness may be increased creasing pH as described inthe art does not ordinarily occur until the pH reaches a value of 4;.5to 5.5 which is the usual approximate location of the point where thehardness ceases to decrease and begins to increase with increases in pH.This known increase in hardness with increasing pH above 5.5 in theusual baths is so rapid, however, and the hardness is so sensitive tominute changes in pH, that in the past adjust- :5; merit of the pH hasnot been considered practical as a means for controlling the hardness ofthe deposit. The increase of hardness with increase of pH in the presentprocess is sufficiently gradual that adjustment of pH constitutes arather sensitive control of hardness.

Alternatively, as is apparent from the formula; the conditions can beadjusted to give deposits of greater or lesser hardness without making 7any change in the composition or acidity of the bath. For instance,increased hardness can be secured by decreasing the current density orvice versa, which is the reverse of the effect noted by some observerswhen using baths of composition slightly different from that hereindisclosed. Otherwise the hardness can be increased by increasing thedegree of agitation. So far as I am aware this effect of varying thedegree of agitation has never been observed in the use of the prior artnickel plating baths. 1' find, however, where it is desired to producenickel deposits having closely specified physical properties, that thisis frequently a convenient method of securing the desired hardness ofthe deposit. If, when a run is started, tests of the hardness show afailure to meet the specifications, it is usually a simple matter tochange the degree of agitation and this alone is often adequate to makethe desired correction without changing any of the more diflicultlyalterable conditions. If it is not sufficient, an additional change incurrent density will generally serve to complete the adjustment, if thecomposition of the bath has been suitably chosen at the start.

Ascan be seen from the formula, the lower the current density thegreater the increase in hardness which results from a given decrease incurrent density. This is particularly the case at high ratios of formateto-total nickel and with vigorous agitation. This fact must be borne inmind in the practice of the process of the present invention. It isespecially significant when making deposits on irregularly-shapedsurfaces. Un less suitable precautions are taken in such cases,

the current density in deep depressions and sharp re-entrant angles maybe but a fraction of that at the high points on the surface. Theresulting dilferences in hardness of the deposit in the high and lowareas may become intolerable and in ex tried do not result in a depositof the specified treme cases the deposit in the lowest areas may becomeso hard and brittle that spontaneous cracking occurs. To avoid thesedifliculties when deposits of irregular shape are to be made,'thecurrent density should be equalized so far as possible over the entiresurface of the cathode by suitable known methods, and the formate tonickel ratio and the degree of agitation kept low enough that theunavoidable variations in current density do not cause excessivevariations in hardness.

Nickel sulfate and nickel chloride are the primary nickel-carryingingredients of the Watts bath. For purposes of the present invention,ratio of nickel sulfate (NiSO4'7H2O) to nickel chloride (NiClz-GHzO) inthe bath is not critical,

as satisfactory results have been obtained With solutions wherein thisratio differed as greatly as from about 2/1 to about 8/1. This ratiodoes,

however, appear to have some effect on the hardness of the deposit,greater proportions of chloride tending to yield harder deposits andsmaller proportions of chloride tending to yield softer deposits. Notonly the ratio between the amounts of these ingredients but also thetotal amount of each may be varied considerablyin aerate:

operations under this invention. baths having a total nickel (Ni)content as high as 66 and as low as 32 grams per liter having been usedsuccessfully, though the actual limits for practical open ation areapparently considerably wider.

The presence of boric acid in the bath appears to stabilize conditionssomewhat and to make for more. uniform deposition, but its precise modeoil functioning is obscure. It does not appear to act as a buffer in therange of pH that I'employ, though that is commonly considered to be itsfunction in the usual Watts bath. If desired, the boric acid may beomitted entirely but I prefer to use from about to about grams perliter.

Formates have in the past been used occasionally in nickel plating bathsas buffers andbrightening agents. The proportions used have not beenconsidered critical and so far as I am aware, formates have never servedthe purposes or the present invention as a control of the "physicalproperties of the deposit. In the present inven tion the ratio of theweight of formate; computed as the formic acid radical (COOH) to theweight of the total nickel (Ni) in the bath, is one of the primaryfactors used in the control of the physical properties of the nickeldeposit and should accordingly be properly chosen at thestartand shouldbe carefully maintained throughout the time of deposition.

In general the most desirable temperaunesare round between and F. thoughthe usable range of temperatures appears to be quite wide-- temperaturesfrom about 110 up to about F. having been used successfully. Thesefigures, however, do not appear to constitute definite limits though itis found that at temperatures much above 160 F. the vaporization offormic acid becomes excessive and at temperatures much below 110 F. theuseful range of current density becomes unduly restricted.

Though the invention is not necessarily limited its use tonon-contaminated solutions, the re sults herein described are thosewhich have been secured in solutions substantially free fromcontaminants, the effects of which in the deposition of nickel are wellknown. Ammonium, sodium,

and potassium ions, for example, have the effect of hardening thedeposit and if present in considerable proportion in the bath mayincrease the hardness beyond the range contemplated in the presentinvention. It may be noted in particular that, because of thedeleterious effect of lead in the solution and because of the solubilityof lead in formic acid, lead-lined tanks and equipment should beavoided. Suitable rubber lined tanks and equipment are recommended-forcontaining the solution, and high silicon iron has been foundsuitablefor pipes, pumps, etc. It is well to continuou'siy filter andpurify the solution during electrodeposition. In this connection the useof activated charcoal or clay has sometimes been found advantageous.Copper, zinc, etc. may be removed from the bath, before using, by knownmethods which employ low current density electrolysis.

During the deposit-ion the composition of the bath tends to change.Ordinarily the nickel concentration tends to build up due to the difference between the anode and cathode efiiciencies.

This in itself is not harmful but the correspondthe decrease in theacidity should be compensated by periodic additions of acid-su1furicacid is satisfactory for the purpose-4:1 order to maintain the pH valuewithin the required limits; The forl'l'iat to-tota-l nickel ratioshould' also be carefully 6 watched and may be controlled by addition offormic acid when necessary due to increase of nickel. content,volatilization of the formic acid, orto other cause. a I The followingexamples will. serve to illustrate the practical use of the invention.

Example 1.--A precision machine part of considerable size and value hadbeen rejected because a cylindrical bearing surface about 4 inches indiameter and 3 inches long had been machined to a diameter slightly lessthan the specified low limit. The part was made ofchrome-nicke1-molybdenum alloy steel heat treated to give it a RockwellC hardness of about 32. (corresponding approximately to a Vickershardness of about 305', in accordance with pub.- lished conversiontables) to resist the extreme loads and vibration towhich it would besub- .iected in use, and it was required that the repaired surface havesubstantially the same hardness. In order to salvage the part, thecylindrical bearing surface was built up slightly above and ground downto the correct dimension, using the present invention to give a depositof nickel having hardness substantially the same as that of the steelitself. For this urpose a plating bath of the following composition wasused:

NiSQr'THzO -grams 158.94 NiCIz-GHzO l do 53.64 NiCCOOH)2'2H2O do..-31.65 H3130: do 25.61 Water liter 1 The total nickel in the bath wasapproximately 57.5 grams per liter and the ratio of formats to total;nickel was approximately 0.268. After preparing the base metal .so thatthe electro-deposited nickel would adhere strongly thereto,

nickel was deposited from this bath onto the undersized cylindrical.surface. During the deposi tion the pH of the bath was maintained at avalue between 2.75 and 2.80 and the temperature at about 140 R, thecathode current density was maintained at 100 amperes per square footwithin close limits and a substantially constant condition of turbulencewas maintained in the solu tion. After about two hours the deposit hadreached a sufficient thickness of about 0.010 inch. When tested, thedeposit showed the desired hardness of from 31 to 33 on the Rockwell Cscale (corresponding approximately to Vickers hardness values betweenabout 296 and 316). When dressed to the required dimensions the part ofhardness on the Rockwell C scale. Had a test deposit not shown hardnesswithin the specified limits, the degree ofagitation and if necessary thecurrent density, could have been altered to give the required degree ofhardness, before starting deposition on the part to be salvaged.

' Example 2.--This example involves the electrolytic production of along strip of sheet nickel =7 for makingran endless belt for use as acasting surface for films or coated paper. The hardness and tensilestrength of strips for this use are desirablyhigh, but they must not beso high as to unduly decrease ductility and increase brittleness.Accordingly the plating bath consisted of 2900 gallons of solutionprepared in the following proportions: V

NiSO4-7H2O grams 185 NiCla-GHzO d O 45 Ni(COOH)2-2H2O "do-" 35 H3303 d30 Water liter 1 Thetotal nickel in the bath was approximately 61 gramsper'liter, and the ratio of formate to total nickel was approximately0.280. The pH of the solution was adjusted to 2.70 by the addition ofsulfuric acid. A good grade of chemicals was used and care was takenthroughout: to prevent contamination of the bath.

The cathode was in the form of a horizontally mounted cylinder 4 feet indiameter and 6 feet in length. The face was composed of l8'8 stainlesssteel containing 2 per cent oftmolybdenum, as described and claimed inmy co-pending application Serial No. 538,537, filed'June 2, 1944, nowabandoned. This face was carefully polished to a mirronfinish. Thiscathode was continuously rotated on its axis at a surface. speed ofabout three feet per hour. The-cathode was rotated in a rubber-linedtank containing the solution described to a depth to submerge about 85per cent of the cylindrical surface. The anodes were in the form ofrolled oval bars of nickel con- 'taining about 2 per cent of cobalt,spaced about inches from the face of the cathode and'bent to' conform toits cylindrical form, each 'bar being enclosed in a woven bag to preventcontamination of the solution. The tank was provided with inlet andoutlet pipes through which the solution was circulated at the rate ofabout 35 gallons per minute by means of a Duriron pump. This, togetherwith air agitation, provided" moderately vigorous agitation(corresponding toa value of A of about 1.4) in the liquor between theelectrodes.

A rubber-covered plate and frame filter contain- 1 temperature at thedesired value. The electrodes 6 were connected to a direct currentgenerator which supplied direct current at. a potential of 9-10 voltsand a rate of about 60 amperes per square foot of the submerged surfaceof the "cathode' As the cathode surface'emerged from .the plating bath,the electrodeposited nickel was "stripped therefrom as a continuousstrip six feet wide and about 0.010 inch thick and was wound on a reel.During the 'run which lasted about 60 hours, a strip of nickel about 175feet long was produced. It was found to have a tensile strength of about130,000 pounds per square .inch (well within the limits specified forthe strip), with V ltlOll of 4. to 4 per cent, and Vickers hardness ofabout 285 to 290, which corresponds to a Rockwell C hardness of about30. The conditions initially established corresponding, in accordancewith the formula, to a Vickers hardness of about 290, required no changein order to prod ces ip i h r e fieqe r si .8. Example 3.In this casethe bath contained per liter; Grams NiSO4-7H2O NiClz-GI-IzO so 7Ni(COOH)z'-2H2O 27.3

Grams per liter msol-vnz'o 24o NiClz-GI-lzO 45 HsB'Os 30 To this wasadded sufficient formic acid to give a ratio of-formate to, total'nickelof 0.l33,'and enough sulfuric acid to reduce the pH to 2.0. Thedeposition was then carried out at a current density of amperespersquarefoot and a temperature of about lf1U F.,- using only a moderate degreec-f agitation which, as hereinbefore set forth, corresponds to a valueof l for the agitation factor-Ain-the formula. The resulting deposit wasfound to have a Vickers hardness of 146 instead of the value of 1&2expected from the establishment of the stated conditions in accordancewith the formula. This is well within the limits of .error in hardnesstesting and accordingly answers the predetermined requirement.

Example 5.,In this case the deposit was to have a hardness intermediatebetween that of the deposit in Example 1 and that in Example 4; butsomewhat harder than their mean. For this purpose the basic solutionwas; the same as that described'in Example 4, the ratio of formate tototal nickel was the same, but the pH was in this case adjusted to 3.5and the deposition-was carried out at a current density of only 30amperes per square foot at a temperature of about F. The same moderatedegree of agitation as in Example 4 was used in this case, correspondingto a value of 1 for the agitation factor A. The resulting deposit wasfound to have a Vickers hardness of 245 which was essentially the sameas the value of 2 16 predicted to result from the establishment of theconditions named, in accordance with the formula.

While the invention has been described as related to the deposition ofnickel, it is to be understcod as including nickel containing smallpercentages of cobalt, and has been used satisfactorilyinelectrodeposition from commercial anodes which commonly contain somecobalt.

I claim:

1. Inthe electrodeposition of nickel from a bath of the Watts typewherein the nickel sulproportion thereof, and other conditions ofdeposition, in accordance with the degree of Vickers hardness Vspecified for the deposit that and within limits about as follows: theratio F of formate to total nickel between 0.1 and 0.5, the pH between2.0 and 3.5, the current density CD between 120 and 30 amperes persquare foot, and the agitation factor A between 1.0 corresponding tomoderate agitation and 2.0 corresponding to turbulent agitation, andbringing the bath to a temperature of between 1 and 160 deg. Fahrenheit.

2. Method of preparing to make electrodeposits of nickel ofapproximately any predetermined specified hardness within the range ofabout 100 to about 400 Vickers, from a bath of the Watts type which issubstantially free from formaldehyde and from sodium, otassium andammonium ions, and wherein the nickel sulphate and nickel chloride arepresent in a ratio between 2:1 and 8:1, which comprises: including theformate radical to the extent, and making a test deposit under theconditions, determined by the formula:

in accordance with the specified value V of the Vickers hardness, at atemperature between 110 and 160 F., said conditions being within thefollowing limits: the agitation factor A between 1.0 corresponding tomoderate and 2.0 corresponding to turbulent agitation, the ratio F offormate to total nickel between 0.1 and 0.5, the pH between 210 and 3.5,and the current density between 30 and 120 amperes per square foot;then, while holding said conditions within said limits, making at leastone of the following changes: increasing the ratio F of formate to totalnickel in the bath, increasing the pH, decreasing the current densityCD, increasing the agitation A, when greater hardness is required tomore closely approximate said specified hardness, and vice versa, saidchanges being proportioned in accordance with said formula, to thedilference between the value of V specified and that of the testdeposit.

3. Method of making electrodeposits of nickel of approximately anypredetermined specified hardness between about 100 and about 400Vickers, from a bath of the Watts type which is substantially free fromformaldehyde and from sodium, potassium, and ammonium ions, and whereinthe nickel sulphate and nickel chloride are present in a ratio between2:1 and 8:1, which comprises: including the formate radical to theextent, and making a test deposit under conditions, determined by theformula:

in accordance with the specified value V of the Vickers hardness, at atemperature between 1 0 and 160 deg. Fahrenheit, said conditions beingwithin the following limits: the agitation factor A between 1.0corresponding to moderate and 2.0 corresponding to turbulent agitation,the ratio F of formate to total nickel between 0.1 and 0.5, the pHbetween 2.0 and 3.5, and the current density CD between 30 and amperesper square foot; then, while holding said condition within said limits,making at least one of the following changes: increasing the ratio F offormate to total nickel in the bath, increasing the pH, in creasing theagitation A, and decreasing the current density CD when greater hardnessis required to more closely approximate said specified hardness, andvice versa, said changes being proportioned, in accordance with saidformula, to the difference between the value of the hardness V specifiedand that of the test deposit; and thereafter electrodepositing nickelfrom said bath while maintaining the conditions of depositionsubstantially constant throughout the deposition process.

WILLIAM B. STODDARD, JR.

REFERENCE S CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,026,718 Weisberg et al. Jan.'7, 1936 FOREIGN PATENTS Number Country Date 526,966 Great Britain Sept.30, 1940 526,967 Great Britain Sept. 30, 1940 OTHER REFERENCES ModernElectroplating, published by Electrochemical Society, 1942, pp. 250,253. Metal Industry, Feb. 9, 1940, p. 155.

1. IN THE ELECTRODEPOSITION OF NICKEL FROM A BATH OF THE WATTS TYPEWHEREIN THE NICKEL SULPHATE AND NICKEL CHLORIDE ARE PRESENT IN A RATIOBETWEEN 2:1 AND 8:1, WHICH IS SUBSTANTIALLY FREE FROM FORMALDEHYDE ANDFROM SODIUM, POTASSIUM, AND AMMONIUM IONS, THE METHOD OF SETTING UP THEOPERATION TO YIELD DEPOSITS OF A PREDETERMINED SPECIFIED HARDNESSBETWEEN ABOUT 100 AND ABOUT 400 VICKERS, WHICH COMPRISES INCLUDING THEFORM ATE RADICAL IN TEH BATH ADN SO ESTABLISHING THE PROPORTION THEREOF,AND OTHER CONDITIONS OF DEPOSITION, IN ACCORDANCE WITH THE DEGREE OFVICKERS HARDNESS V SPECIFIED FOR THE DEPOSIT THAT,